Evaluation of extreme ozone events over the Iberian Peninsula from Brewer spectrophotometers in the 2000s

The analysis of extreme events is an essential key in the research of the atmospheric ozone due to their importance in biological and radiative effects. Total ozone column (TOC) databases from five ground-based sites equipped with a Brewer spectrometer are used to evaluate extreme ozone events along the Iberian Peninsula for the period 2002-2012. The monthly standard deviation is proved as a reliable metric to identify extreme cases. A total of 465 events (days) are classified as extremes events. For the database used, 2011 presents 32 events with very low TOC values (miniholes), while 2010 is the year with the maximum number (51) of events with very high TOC values (minihighs). The weight of the miniholes (minihighs) over the ozone annual mean can achieve values over the 4% (8%). The relationship between global dynamical features and ozone extreme events is also addressed in this study. Double tropopause events have explained in 2002 and 2004 up to the half of minihole events, while the North Atlantic Oscillation (NAO) negative phase is the condition prevalent in the majority of the minihighs in the entire period. These global characteristics are verified in the analysis of a case study (February-March 2004) exhibiting two periods with double tropopause events and a change in the sign of the NAO index with the consequent change in the tropopause pressure. (C) 2015 Elsevier B.V. All rights reserved.